The present invention relates to an electronically controlled fuel injection apparatus, more particularly to an electronically controlled fuel injection apparatus for stably operating an internal combustion engine without deteriorating the response of the engine.
Electronically controlled fuel injection apparatus in which the fuel injection pump of an internal combustion engine is operatively controlled by use of a microcomputer are in wide use. The conventional electronically controlled fuel injection apparatus of this kind is constructed in such a manner that the deviation between a target or preset amount of fuel injection of the fuel injection pump, calculated in accordance with the operating conditions of the engine, and the actual amount of fuel injection is determined, and a fuel regulating member of the fuel injection pump is controlled in accordance with the result of the determination. An injection apparatus according to this arrangement is disclosed for instance in Japanese Patent Application Disclosure No. Sho 57-49032/82.
In the disclosed apparatus, in order to determine the target amount of fuel injection, a three dimensional map is used for determining the required amount of fuel injection on the basis of data indicative of the engine speed and the amount of operation of an accelerator pedal, and data indicative of the required (target) amount of fuel injection at each instant is calculated by a map calculation using the three dimensional map and an interpolation calculation which is based on the result of the map calculation and is carried out in the operation steps for calculating a basic fuel injection amount executed within a microcomputer.
In the injection apparatus of the kind described above, an improvement in the control response as well as in the stabilization of the engine speed is required. To this end, it is necessary to minimize the control time between the time point at which the engine speed data is obtained and the time point at which the fuel regulating member is positioned at the right position for the engine speed. A well-known system for realizing this involves calculating the target amount of fuel injection in synchronization with the occurrence of the pulses used as the basis for calculating the engine speed. For example, in one such widely used system an interrupt program for calculating the target amount of fuel injection in response to the input of the pulses is employed.
However, when the target amount of fuel injection is calculated on the basis of the three dimensional map by an interrupt program executed in response to the occurrence of the pulses, the interpolation calculation for the three dimensional map becomes so complex that most of the microcomputer's time has to be used for the interpolation calculation and this in turn greatly reduces the number of main program steps that can be executed and as a consequence remarkably lowers the response in other control operations.